What is a THM File?

THM files have gotten complicated with all the conflicting information floating around online. As someone who has spent years dealing with digital media workflows and camera systems, I learned everything there is to know about these little thumbnail files. Today, I will share it all with you.

What THM Files Actually Are

THM stands for Thumbnail. A THM file is a small image — typically JPEG format — that a camera or camcorder generates automatically alongside a video file. Think of it as a preview snapshot. Instead of loading a full video just to see what’s on it, your file browser or media software can display the THM thumbnail instantly.

If you’ve ever browsed video files from a camera and seen little preview images, those were likely generated from THM files. They serve the same function as thumbnails on a website: a quick visual summary so you don’t have to open the full-size content every time.

How They Get Created

Your camera handles this automatically. When you hit record, the device captures a frame from the video — usually one of the first frames — and saves it as a compressed JPEG with a .THM extension. You don’t have to do anything; it just happens in the background.

Probably should have led with this section, honestly, because the naming convention is the key to understanding THM files. They always share the same base filename as their corresponding video. So if your camera saves a video as MOV001.AVI, the thumbnail shows up as MOV001.THM. That naming link is how software knows which thumbnail belongs to which video.

Where You’ll Run Into Them

THM files show up in a few specific contexts:

• Camcorders and Digital Cameras: Especially models focused on video recording. Sony, Canon, and other major manufacturers have used THM files in various camera lines over the years. They’re particularly common on older camcorders and DSLR cameras that shoot video.
• Media Management Software: When you import video to your computer, editing software and media libraries use THM files to generate those grid-view previews. If you’ve ever imported footage from an SD card and seen a nice organized gallery of clips, THM files are often doing the heavy lifting behind the scenes.
• File Browsers: Windows Explorer and similar file managers can display THM-based thumbnails when you browse folders full of video files. That instant visual feedback saves you from opening each clip just to figure out what’s on it.

Under the Hood

People sometimes confuse THM files with video files since they live right next to them on the memory card. But the content is completely different. A THM file is a single still image — a JPEG — weighing in at maybe a few dozen kilobytes. The video file next to it might be several gigabytes.

Because THM files follow the JPEG standard, any image viewer can open them. You don’t need specialized software. Just rename the extension from .THM to .JPG if your image viewer doesn’t recognize the THM extension, and it’ll open right up. What you’ll see is a single frame from the video, usually the first frame or a frame from the first few seconds.

Managing Your THM Files

For most people, THM files just quietly do their job without needing any attention. But when you’re organizing a large media library, it helps to understand a few things about them.

Deleting THM files won’t break your videos. The video will still play fine. What you lose is the thumbnail preview in browsers and media managers that rely on them. If you’re archiving video files and want to keep previews working, keep the THM files alongside their video partners. If storage space is tight (it shouldn’t be — these files are tiny), deleting them is harmless.

When transferring videos from camera to computer, copy the THM files along with the video files. Dragging just the video files and leaving the THM files behind means your media software has to regenerate thumbnails from scratch, which is slower than just using the ones the camera already made.

Common Questions

• Can I delete THM files? Yes. Your videos won’t be affected. You just lose the pre-generated thumbnail previews. Most modern software can regenerate thumbnails on its own, so the practical impact is minimal.
• Do they take up much space? Barely anything. Each THM file is a small JPEG — we’re talking kilobytes, not megabytes. On a 64GB SD card full of video, the THM files combined might use a few megabytes total.
• Are they essential? Not for playing your videos. They’re a convenience feature. But for workflow efficiency — browsing, organizing, selecting clips — they earn their keep.

When You Find One on Your Card

That’s what makes THM files endearing to us media folks — they’re a small, thoughtful touch from camera manufacturers that makes the workflow of managing video footage just a little smoother. If you stumble across a .THM file for the first time, now you know: it’s just a thumbnail, it’s harmless, and it’s there to help you preview your videos without opening them one by one. As digital media keeps growing, understanding these small supporting files helps you stay organized and efficient.